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本刊初二版1998年6月号上的《初二物理竞赛自测题》里,有一道浮力竞赛题.原题是:一个塑料实心球放在水中静止时受到的浮力为28.5牛,放在酒精中静止时受到的浮力为24牛,已知酒精密度为0.8×10～3千克/米～3,求塑料球的密度?此题文句简短,内容精练,题中稳含着塑料球在水和酒精中的浮沉状态.这是一道培养同学分析、比较、推理和演绎等思维能力,以及数理解题方法技巧的好题.比较而言,此题至少有三种简捷解法,现分析如下.解法1 假设水、酒精和塑料球的密度分别为ρ1、ρ2.和ρ;塑料球的体积和自重为V与G,它在水和酒精中排开的体积与受到的浮力分别为V_1、V_2与F_1、F_2.
There was a buoyancy contest in the June 1998 issue of the “Self-Testing of the Junior Physics Competition” in the first issue of the magazine’s 2nd edition. The original title was: A solid plastic ball received a buoyancy of 28.5 N while resting in water. The buoyant force is 24 N when it is still in alcohol, and the known alcohol density is 0.8×10 - 3 kg/m -3. Find the density of the plastic ball. This sentence is short, concise, and contains plastic balls. The floating state of water and alcohol. This is a good question for cultivating the students’ ability to analyze, compare, reason and deduct, as well as the number of methods and techniques for comprehension. In comparison, there are at least three simple solutions to this question. Solution 1 Assume that the density of water, alcohol, and plastic balls are ρ1, ρ2, and ρ, respectively; the volume and weight of plastic balls are V and G, and the volume and buoyancy of the plastic balls that are discharged in water and alcohol are V_1 and V_2, respectively. With F_1, F_2.